"Hydrocarbon conversion reactions" encompass a broad range of both isomerization and oligomerization reactions, many of which are of vital interest to the chemical and petroleum industries. Increasingly, these reactions provide major sources of such petrochemical commodities as toluene and olefin oligomers. Hence, there is a need for improved processes for the preparation of such compounds.
Many of the hydrocarbon conversion reactions of interest to the chemical and petrochemical industries can be catalyzed by suitable acid catalysts. Heterogeneous acid catalysts are generally preferred in such reactions, due to ease of product separation and catalyst regeneration. One particularly attractive class of heterogeneous acid catalysts is that of the perfluorinated ion-exchange polymers which have a substantially fluorinated aliphatic backbone with pendant sulfonic, carboxylic or phosphonic acid groups. These perfluorinated ion-exchange polymers combine relatively high thermal and chemical stability with very high Hammett acidities. The use of such polymers in various hydrocarbon conversion reactions has been reviewed by Waller et al., Chemtech, July 1987, pp. 438-441 and references therein.
Particularly useful in many acid-catalyzed reactions are the perfluorinated ion-exchange polymers containing sulfonic acid groups due to their high acid activity, thermal stability, ease of separation from reaction mixture, and ease of regeneration. Typical examples of such polymers are those described in U.S. Pat. Nos. 3,282,875; 3,624,053; 3,849,243; 4,038,213; 4,303,551; or 4,661,411. Blends and laminates of perfluorinated polymers having sulfonic acid groups with other polymers are also known.
U.S. Pat. No. 4,176,215 teaches ion-exchange films, membranes and laminar structures incorporating a layer of a blend of a first fluorinated polymer containing sulfonyl groups in ionizable form with a second fluorinated polymer containing carboxylic acid functional groups. Such films and membranes are used in chloralkali electrolysis cells.
U.S. Pat. No. 4,433,082 discloses a process useful in recovering perfluorinated polymers having sulfonic acid or sulfonate groups from scrap and used articles containing such polymers Example 7 teaches a scrap membrane having one layer of a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) in --SO.sub.3 H form and one layer of a copolymer of tetrafluoroethylene and methyl perfluoro(4,7-dioxa-5-methyl-8-nonenoate) in --COOCH.sub.3 form and a reinforcing fabric of polytetrafluoroethylene.
U.S. Pat. No. 4,591,439 discloses an ion-exchange device with cation exchange membranes of perfluorinated polymers having sulfonyl functional groups. Preferably the polymers are present as copolymers with tetrafluoroethylene or tetrafluoroethylene and hexafluoropropylene.
European Patent Application 291,033 published Nov. 17, 1988, discloses use of perfluorinated acid ion-exchange resins as effective catalysts for the isomerization of 3-pentenoic compounds to 4-pentenoic compounds. Blends of perfluorinated sulfonic acid and perfluorinated carboxylic acid polymers are employed. Preferred are blends of tetrafluoroethylene copolymers with methylperfluoro-5-methyl-4,7-dioxanon-8-eneoate and tetrafluoroethylene copolymers with perfluoro-(3,6-dioxa-4-methyl-7-octene)sulfonic acid, each containing 0.1 to 4% of a noble metal in an oxidation state of at least +2 incorporated into the polymer.
Kapura et al., "Sulfonated Polymers as Alkylation Catalysts", Industrial Engineering Chemistry Product Research Development, Vol. 12, No. 1, pp. 62-66 (1973), disclosed that a sulfonated fluorocarbon vinyl ether polymer was inactive in alkylating isobutane with propylene in the gas phase and in a mole ratio of 5 to 1 at 260.degree. C. The conclusion reached in that study was that the sulfonated fluorocarbon vinyl ether polymer catalyst was too weakly acidic to catalyze paraffin alkylation and that the polymer was not a useful catalyst. That study also showed that these same ion-exchange resins were useful in the alkylation of benzene with propylene in the vapor phase to form cumene. However, the conclusion reached by Kapura and Gates with regard to the formation of cumene was that the sulfonated polymer was not "a particularly useful catalyst at temperatures greater than about 150.degree. C."
A major disadvantage of these polymers, however, is their relatively high cost. A need exists, therefore, to develop cheaper and/or more active catalysts which retain the high thermal and chemical stability of the perfluorinated ion-exchange polymers.
This invention provides improved processes for selected hydrocarbon conversion reactions, wherein the improvement is the use of a catalyst which is a blend of a perfluorinated ion-exchange polymer with pendant --SO.sub.3 H groups and an inert perfluorinated polymer diluent in a nonpolar reaction mixture. This diluted catalyst blend is unexpectedly more active on an acid-equivalent basis, and hence less expensive to use, than the perfluorinated polymer with --SO.sub.3 H groups alone.